#### 4.7Blur

 procedure(flomap-gaussian-blur fm xσ [yσ]) → flomap fm : flomap xσ : Real yσ : Real = xσ
Returns fm convolved, per-component, with an axis-aligned Gaussian kernel with standard deviations and .

If perfect Gaussian blur is not important, use flomap-blur instead, which approximates Gaussian blur closely and is faster.

Examples:

 > (flomap->bitmap (flomap-gaussian-blur (flomap-inset fm 12) 4)) > (flomap->bitmap (flomap-gaussian-blur (flomap-inset fm 12 3) 4 1))

 procedure fm : flomap σ : Real
Returns fm convolved, per-component and per-row, with a Gaussian kernel with standard deviation σ.

If perfect Gaussian blur is not important, use flomap-blur-x instead, which approximates Gaussian blur closely and is usually much faster.

Example:

 > (flomap->bitmap (flomap-gaussian-blur-x (flomap-inset fm 12 0) 4))

 procedure fm : flomap σ : Real
Like flomap-gaussian-blur-x, but per-column instead of per-row.

 procedure(flomap-box-blur fm x-radius [y-radius]) → flomap fm : flomap x-radius : Real y-radius : Real = x-radius
Returns fm convolved, per-component, with a box kernel with radii x-radius and y-radius. The radii are of the largest axis-aligned ellipse that would fit in the box.

Examples:

 > (flomap->bitmap (flomap-box-blur (flomap-inset fm 4) 4)) > (flomap->bitmap (flomap-box-blur (flomap-inset fm 4 1) 4 1))

 procedure(flomap-box-blur-x fm radius) → flomap fm : flomap radius : Real
Returns fm convolved, per-component and per-row, with a box kernel with radius radius.

Example:

 > (flomap->bitmap (flomap-box-blur-x (flomap-inset fm 4 0) 4))

 procedure(flomap-box-blur-y fm radius) → flomap fm : flomap radius : Real
Like flomap-box-blur-x, but per-column instead of per-row.

 procedure(flomap-blur fm xσ [yσ]) → flomap fm : flomap xσ : Real yσ : Real = xσ
Returns approximately the result of (flomap-gaussian-blur fm ).

Gaussian blur, as it is implemented by flomap-gaussian-blur, is O( + ) for any fixed flomap size. On the other hand, flomap-blur is O(1) for the same size.

Examples:

> (define gauss-blur-fm (time (flomap-gaussian-blur fm 12)))

cpu time: 252 real time: 254 gc time: 0

> (define blur-fm (time (flomap-blur fm 12)))

cpu time: 103 real time: 104 gc time: 18

 > (flomap-extreme-values (fmsqr (fm- gauss-blur-fm blur-fm)))
 0 0.0031727

 procedure(flomap-blur-x fm xσ) → flomap fm : flomap xσ : Real
Like flomap-blur, but blurs per-row only.

 procedure(flomap-blur-y fm yσ) → flomap fm : flomap yσ : Real
Like flomap-blur, but blurs per-column only.